This invention relates to lead frames for packaging solid state chips such as triacs or transistors and to packaged chips having integral terminal members connected to the chips for making external connections.
Solid state devices such as transistors and triacs are commonly incorporated into electrical circuits by connecting the contact areas of the chip to sheet metal stamped and formed leads in a lead frame which, in turn, have portions which can be connected to external circuitry. The sheet metal lead frames are produced in endless strip form. The final package for the chip is thus produced by mounting the chip on a chip receiving portion of the lead frame, connecting conductors of the lead frame to the chip, and then encapsulating the chip and portions of the conductors in a suitable insulating material such as an epoxy resin. The portions of the conductors which extend externally of the encapsulating or potting material are then connected to further conductors to connect the encapsulated chip into a circuit.
Usually, solid state devices are incorporated into circuits which are contained on a printed circuit board and the leads which extend from the packaged solid state device are relatively small so that they can be inserted into holes in a printed circuit board and soldered to conductors on the printed circuit board. The electrical connections between the chip and the conductors of the lead frame are commonly made by wires which are bonded to the chip and to the ends of the conductors although some lead frames have been proposed which permit direct bonding of the lead frame to the chip; see, for example, U.S. Pat. Nos. 3,650,232, 3,735,017, and 3,736,367. The lead frames shown in these patents have parallel side-by-side terminal post portions which are dimensioned such that they can be inserted into the holes in a printed circuit board as mentioned above.
Under some circumstances, solid state chips are used in circuits which are not on printed circuit boards but which are rather compressed of conventional insulated wires. For example, there is a trend towards the use of solid state control components in domestic appliances such as washers, dryers, microwave ovens, and conventional ranges. Such appliances require insulated wires for many of their elements, such as the heating units, and the control circuits and the electrical connections required for appliances are achieved by means of conventional harnesses composed of insulated wires having disengageable terminals on their ends. Many, if not most, of the prior art packaging methods for solid state chips can not be readily incorporated into appliance harnesses for the reason, as mentioned above, that the packaging methods result in relatively thin leads in the solid state package which are suitable only for use on printed circuit boards.
The present invention is directed to the achievement of a package for a transistor or the like having relatively massive terminals which can be mated with complementary terminal devices on insulated wires. The invention is further directed to the achievement of a lead frame which can be produced in the form of a continuous strip and which is suitable for use in packaging solid state chips in a way which will result in the completed package having terminals suitable for mating with complementary terminals on wires.
In accordance with a preferred embodiment of the invention, a continuous strip of lead frames comprises a carrier strip having three integral arms extending laterally therefrom for each lead frame. One of the arms has a chip supporting surface and the other two arms have reversely bent portions which extend over this surface so that a chip mounted on the chip supporting surface will be contacted on its underside by the chip supporting surface and on its upper side by the remaining arms. Each of the arms formed has extending therefrom a tab portion which lies in the plane of the strip and which is composed of a double thickness of the metal of the strip. In use, after the chip is mounted on the chip supporting surface, a substrate is provided under the arms and the arms are separated from the carrier strip so that they then provide independent electrical bands to the chip. The arms are then bent through an angle of 90.degree. so that they surround the chip and extend normally of the substrate. Finally, the base portions of the terminal tabs which are adjacent to the heat snk and the chip are encapsulated and enclosed in suitable insulating housing means. The resulting package then has three terminal tabs extending therefrom which can be mated with complementary terminal devices.
It is accordingly an object of the invention to provide an improved lead frame strip in which each lead frame has improved terminal means integral therewith. A further object is to provide an improved finished package for a solid state chip such as a transistor. A still further object is to provide an improved method of packaging solid state chips or the like.